1. Field of the Invention
The present invention relates to a control system for an adjustable damping force damper and, more particularly, a control system for an adjustable damping force damper for controlling a rolling motion of a car body at a time of turning.
2. Description of the Background Art
The spring provided to the suspension apparatus of the vehicle is deformed while absorbing a shock, and springs back in the direction to restore the deformation when an external force disappears. As a result, a reciprocating oscillation is generated. In order to attenuate an oscillation energy of this spring, a damper called the so-called shock absorber is used together in the suspension apparatus of the vehicle. Preferably a damping force of this damper should be set small to lessen a shock, but preferably such damping force of the damper should be set large to some extent to enhance a road-holding performance and a controllability of a tire. As the damper that is able to satisfy these exclusive conditions, an adjustable damping force damper capable of changing a damping force has been known (see Japanese Patent Unexamined Publication No. JP-A-60-113711).
In the meanwhile, the technology to enhance the roll stiffness during a turning operation by controlling a damping force of the damper of each wheel individually in response to a rate of change in lateral acceleration has been known (see Japanese Patent Unexamined Publication No. JP-A-11-115440). Here it is common that the lateral acceleration is sensed at a gravity point of the car body. In order to compensate for a difference in phase caused by the fact that a lateral acceleration sensing point is separated from the axle whose motion must be controlled actually, it is commonly conducted to add a derivative value of the yaw rate to control parameters.
Consequently a responsibility can be improved by leading a phase by using the derivative value of the yaw rate. On the contrary, only when a phase is led simply to improve the control responsibility of the damping force in such a driving situation such as winding road running or slalom running, for example, that the vehicle is running by turning a steering wheel rightward/leftward continuously, a directivity of a controlled target value of the damping force is reversed immediately before a turning angle of the tire passes through a neutral point. For this reason, in case the outer wheel moving on a turning circle is considered, actually the damper must continue to stand still firm, nevertheless the driver feels as if such damper lost its withstanding power. As a result, it is possible that such situation leads the driver to feel a peculiar feeling as if the damper breaks down unexpectedly for an instant.